PEX Home Run vs recirculating loop?

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Anthony W

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Our master shower is located roughly 60 feet from our hot water heater (pipe length). Knowing this may be an issue, I added a hot water recirculating loop when we built our house in 2003. It works fine, but with our varying schedule the pump runs 4-5 hours in the morning, and another 4-5 hours in the evening. That wastes a lot of energy, as well as pump noise and maintenance issues. We are also considering a heat pump water heater in the future, which I've heard don't work well with recirculating systems.

I currently have a CPVC 3/4" main trunk line, with 1/2" CPVC stubs to each fixture. The return line is 1/2" from the furthest shower. Without the pump running, it can take well over a minute for hot water to reach the master shower (low flow shower heads). With the pump running that is reduced to 5-10 seconds or so (I assume this is the water in the 1/2" stub up from the recirculation loop).

I've tried a number of "on demand" triggers for the pump, but it still takes about a minute for the hot water to circulate through the loop before it's hot at the shower. No significant difference from not using the pump at all.

I'm curious if running a dedicated 1/2" PEX "home run" directly from the water heater to the shower would allow reasonable wait times without needing the recirculating system? What about a 3/8" home run line? We have two showers in the master bath. Would one 1/2" line serve both, or would two 3/8" lines be better?

Would love to hear other's experience with home run systems.

Thanks!
 

John Gayewski

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What's your static pressure? A 60' run of 1/2" pipe vs a 60' run of 3/4" with 1/2" mixed in will not be significantly different but there will be some difference in wait time. The main question would be will it significantly change the quality of the shower? Which can be calculated. 3/8" pipe isn't legal to run so that's out.

I'm curious why you think the pump wastes "a lot" of energy? The cost to run a small pump like that (guessing you don't have a huge pump) is maybe $20 per year. That's with it running constantly which is how pumps like to run. A pump that goes on and off a lot will ruin itself.

You either waste water, or energy. With a circulation system your only wasting energy in the summer when you don't want to add heat to the house. Changing from 3/4 to 1/2 isn't going to significantly change how much water you waste.
 

Anthony W

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We're on a private well. Haven't tested at the house, but pressure is about 40-60psi at the well.

As to waste, yes, I meant the heat loss from the pipe, though I suppose the pump adds a bit too.

I was just researching ways to reduce the wait time without needing the recirculating system. It works fine, though there is some maintenance and complexity that isn't exactly wife friendly. I've also read they often don't work well with heat pump water heaters.
 

JoeJee

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We're on a private well. Haven't tested at the house, but pressure is about 40-60psi at the well.

As to waste, yes, I meant the heat loss from the pipe, though I suppose the pump adds a bit too.

I was just researching ways to reduce the wait time without needing the recirculating system. It works fine, though there is some maintenance and complexity that isn't exactly wife friendly. I've also read they often don't work well with heat pump water heaters.
My understanding w/ HP water heater and some on demand water heaters is you use a small electric WH in the loop instead of the main WH.

Are your Hot water lines and return lines insulated?
 
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